b 1. Field of the Invention
This invention relates to fuel control systems for dual chamber stratified charge engines and particularly to fuel control systems of the type described which can utilize single point fuel induction for the main (lean) mixture in combination with multi-point fuel injection for the igniting (rich) mixture.
2. Description of the Prior Art
Stratification of the air-fuel charge to internal combustion engines has long been recognized as an effective way of generally improving combustion and/or reducing engine exhaust air pollutants i.e., carbon monoxide (CO) unburned hydrocarbons (HC) and oxides of nitrogen (NO.sub.x) by permitting lean, controlled combustion. The most effective implementation of the stratification principle in spark ignited engines currently on production vehicles is the dual chamber system developed by the Honda Motor Car Company and identified as their Compound Vortex Controlled Combustion System (CVCC). A system of this type is described in the July, 1973 issue of Science and Mechanics, pages 40-43 and in the April, 1974 issue of Road and Track, pages 32-36. In essence, the Honda CVCC approach provides the capability of effectively burning a lean airfuel mixture by spark igniting a rich mixture in a small pre-combustion chamber and using the burning rich mixture to ignite a much larger volume of the lean mixture in a main combustion chamber. Thus, "spark ignition" is supplemented with "torch ignition" allowing the combustion of lean mixtures at air-fuel ratios far above those normally experienced with conventional spark ignition only. In addition to achieving a substantial reduction in the aforenoted exhaust emission components without the need for add-on exhaust treatment equipment, good fuel economy and low system costs can be achieved under conditions of proper control and proportioning of the rich and lean mixtures.
Essentially, then, in dual chamber stratified charge engines such as the Honda CVCC engine, the fuel control system must function to provide suitable lean and rich mixtures to the main and pre-combustion chambers, respectively, of each engine cylinder in response to the driver's command and other necessary inputs. It must further be realized that a dual chamber stratified charge engine system is therefore significantly different in relation to fuel management than a conventional internal combustion engine. In particular, small quantities of a rich mixture must be generated and distributed while large quantities of a lean mixture must be generated and distributed. Further, the rich and lean mixtures must be optimally coordinated for best system performance.
The system of the invention is well suited for the purposes described in that it utilizes single point induction for the main lean mixture in combination with multi-point fuel injection for the igniting rich mixture. The advantages accruing from such a combination include the most precise generation and distribution of the rich mixture required in the pre-chamber and the most efficient generation and distribution of the lean mixture required in the main chamber. Further, use of fuel injection in association with the pre-chamber can allow significant simplification of the pre-chamber intake manifolding as in advantageous in multicylinder engines.